Light-fraction based fuel composition for compression ignited engines

ABSTRACT

A light fraction fuel composition for compression-ignited engines comprises about 25 v/v % to about 50 v/v % commercial diesel fuel; about 40 v/v % to about 69 v/v % straight run heavy naphtha about 5 v/v % to about 10 v/v % n-butanol; and about 0.2 v/v % to about 1.7 v/v % 2-Ethylhexyl nitrate. The relative percentages of commercial diesel fuel and straight run heavy naphtha are controlled to obtain a cetane number of at least 51 for a selected engine.

FIELD OF THE INVENTION

The present invention relates to petroleum-based fuels, and in particular, relates to a light-fraction based fuel composition for compression ignited engines.

BACKGROUND OF THE INVENTION

Environmental regulations and policies increase the impetus to reduce fossil fuel combustion emissions. Compression-ignition (CI) vehicles face added pressure to reduce emissions due to potential competition from battery-electric vehicles (BEV) and natural gas trucks, which have lower emission profiles. Attempts have been made to develop fuels that produce fewer emissions, including carbon dioxide, aromatic hydrocarbons and soot. However, due to the specific requirements of diesel compression ignitions in terms of vapor pressure and cetane number, it has proven difficult to develop drop-in replacements for diesel fuel that reduce such emissions, while maintaining the suitable operability, safety and maintenance characteristics suitable for a CI engine.

There is therefore a continued need for the development of drop-in replacement fuels for commercial diesel that can improve the emission profiles of diesel engines.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a light fraction fuel composition for compression-ignited engines that comprises about 25 v/v % to about 50 v/v % commercial diesel fuel; about 40 v/v % to about 69 v/v % straight run heavy naphtha about 5 v/v % to about 10 v/v % n-butanol; and about 0.2 v/v % to about 1.7 v/v % 2-Ethylhexyl nitrate.

Preferably, the relative percentages of commercial diesel fuel and straight run heavy naphtha are controlled to obtain a cetane number of at least 51 for a selected engine, and the relative percentages of commercial diesel fuel and straight run heavy naphtha are controlled to obtain a Reid vapor pressure in a range of about 7.28 PSI and about 10.88 PSI for a selected engine.

In some embodiments, the relative percentages of commercial diesel fuel and straight run heavy naphtha are controlled to obtain a boiling point range of about 30 C (initial) to about 350 C (final).

In one implementation, the light fraction fuel composition includes about 26 v/v % commercial diesel, about 68 v/v % straight run heavy naphtha, about 5 v/v % n-butanol and about 1.0% 2-Ethylhexyl nitrate.

In another implementation, the light fraction fuel composition includes about 45 v/v % commercial diesel, about 49 v/v % straight run heavy naphtha, about 5 v/v % n-butanol and about 1.0% 2-Ethylhexyl nitrate.

In another embodiment, the light fraction fuel composition for compression-ignited engines comprises about 0 v/v % to about 50 v/v % commercial diesel fuel; about 40 v/v % to about 95 v/v % straight run heavy naphtha about 5 v/v % to about 10 v/v % n-butanol; and about 0.2 v/v % to about 1.7 v/v % 2-Ethylhexyl nitrate.

These and other features can be appreciated from the accompanying description of certain embodiments of the invention which are discussed in relation to the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing a relationship between viscosity and the percentage of light fraction in the fuel composition.

FIG. 2 is a graph showing the evaporated volume fraction by distillation temperature for the three fuel variants.

DETAILED DESCRIPTION CERTAIN OF EMBODIMENTS OF THE INVENTION

Embodiments of the present invention provide a fuel composition for compression ignition engines that includes about 40 volume percent (v/v %) to about 94 v/v % straight run heavy naphtha (referred to as the “light fraction”), about 0 v/v % to about 50 v/v % commercial diesel fuel, about 5 v/v % to about 10 v/v % n-butanol, and about 0.2 v/v % to about 1.7 v/v % 2-EHN (2-ethylhexyl nitrate). Fuel variants having different blends within these ranges were tested on conventional CI engines. Through these tests it has been determined that blends of light fraction with commercial diesel can be used as drop-in replacements for commercial diesel that yield reduced carbon dioxide and soot emissions.

In developing the fuel composition of the present invention, several initial operating parameter targets were specified to ensure that the fuel composition would meet standard diesel operating, safety, and maintenance requirements. A Cetane number of 51 was selected, which is within the normal diesel operation range. The Cetane number is a measure of how fast the fuel auto-ignites under pressure. Vapor pressure in the range of 50.33 to 75.15 kPa was selected to avoid a combustible tank mixture. A lubricity value below 460 μm was chosen to minimize metal wear on sliding components, and a viscosity above 2 cSt was selected to ensure fuel injection system durability.

It was understood that by blending diesel with a percentage of light fraction straight run naphtha, which has higher LHV (lower heating value) and a higher hydrogen to carbon ratio (H/C) than commercial diesel fuel, lower CO₂ emissions could be achieved for the same thermodynamic efficiency. In addition, straight run naphtha has a lower polyaromatic hydrocarbon content than commercial diesel fuel. As polyaromatic hydrocarbons are often soot (smoke) precursors, by reducing their content, it is possible to decrease the smoke out of the engine without altering emissions of NO_(x), HC and CO. Importantly, testing has shown that variants of the novel fuel met targeted specifications without sacrificing any of the desired properties required for a drop-in fuel for compression-ignition engines. Additionally, the light fraction fuel composition of the present invention provides economic benefits in terms of improved refinery margins.

Tests were performed on three-different fuel variants. The variants were tested on both Volvo MD11 Euro V and Modern Cummins ISX15 CI engines as drop-in diesel replacement fuel. The first test used a fuel variant with 75% light fraction/25% commercial diesel, and is referred to as test GD75; a second test used a fuel variant with 50% light fraction/50% commercial diesel is referred to as test GD50; and a third test used a fuel variant that contained no diesel fraction, and is referred to as GD100 (these percentages reflect relative percentages of light fraction and diesel, and do not count other components such as n-butanol).

FIG. 1 is a graph showing a relationship between viscosity and the percentage of light fraction in the fuel composition. As the graph of FIG. 1 indicates, to reach the targeted viscosity requires a light fraction percentage of at most 20%. However, testing using a blend of 50% light fraction and 50% diesel (GD50) over a 1200-hour period yielded positive results, with no damage to the engine or fuel injection system. As a consequence of these experimental results, the initial viscosity specification of 2 cSt was lowered to 1 cSt, and a second GD50 blend was tested. GD100, which contained no diesel fraction, was tested as a control to determine maximal reduction levels of CO₂ and particulates. FIG. 2 is a graph showing the evaporated volume fraction by distillation temperature for the three variants. This graph shows that the greater fraction of diesel present, the greater fraction remains unevaporated over the 50 to 300° C. span. For example, at 200° C., approximately 50 percent of GD50 (variant with the highest diesel percentage) evaporates, whereas, at the same temperature, all of the GD100 evaporates, and approximately 80 percent of GD75 evaporates. This can be explained by the fact that the lighter straight-run naphtha component evaporates at lower temperatures than the heavier diesel component. Table I lists the main properties of the three tested fuel variants.

TABLE I GD100 GD50 (100% light GD75 (75% light (50% light fraction) fraction) fraction) Cetane Number 51.2 51.8 51.7 Density (15° C.) (kg/L) 0.7177 0.7477 0.7746 Vapor Pressure at 69.3 58.9 62.9 37.8° C. (kPa) Cloud Point −76 −24 −16 Viscosity at 40° C. (cSt) .598 .797 1.083 Polycyclic Aromatics 0.1 1.9 3 Content (% m/m) Total Aromatics 6.3 12.1 17.5 C (% m/m) 85.14 85.7 86.23 H (% m/m) 14.86 14.3 13.77 O (% m/m) 0 0 0 Heating Value (MJ/kg) 43.78 43.86 44.17 2-EHN (% v/v) 1.7 1 0.75 n-butanol (% v/v) 10 7.5 5 n-paraffins (% v/v) 31.6 n.a. n.a. iso-paraffins (% v/v) 44.3 n.a. n.a. olefins (% v/v) 0.4 n.a. n.a. naphthenes % v/v) 14.9 n.a. n.a. aromatics (% v/v) 7.1 n.a. n.a. unknown (% v/v) 1.7 n.a. n.a.

Table II lists the minimal and maximal values (range) of properties across the three tested fuel variants. Any final blend formulation within the ranges set forth below will be engine-specific and depend on the experimental performance and durability of the fuel injection system of the specific engine type.

TABLE II Component Minimum Maximum Straight run naphtha [%] 50 100 Commercial diesel [%] 0 50 Ignition enhancer [%] 0.5 2 n-butanol [%] 5 10 Initial Boiling Point [° C.] 30 35 T50 (50% volume distilled) [° C.] 110 197 T90 (90% volume distilled) [° C.] 165 340 Density [kg/L] .7115 .775 H/C Ratio 1.9 2.15 LHV [MJ/kg] 43.7 44.2 Cetane Number 51 52 PAH (polycyclic hydrocarbons) [%] 0 3 Aromatics [%] 5 20 Reid Vapor Pressure [kPa] 58 63 Viscosity [cSt] 0.5 1.1

Table III lists experimental emission results of tests performed on the Volvo MD11 compression ignition engine in terms of relative variation from a 100% diesel baseline. The Volvo tests included both drop-in replacement tests, and tests performed using optimized injection settings in order to understand the potential of the fuel variants. A notable feature of the results of the Volvo engine tests is that when light fraction is blended with commercial diesel as a drop-in replacement without optimization, NO_(x) emissions decrease but soot emissions increase and efficiency slightly decreases for all variants. However, when injection settings are optimized, NOx emissions are largely unchanged, while soot emissions markedly decrease and efficiency marginally increases, particularly for GD75 and GD100. These results show that soot emissions can be reduced at approximately constant NO_(x) and efficiency.

TABLE III Drop-in Replacement Optimized (constant software software settings settings) for injection NO_(x) Soot Efficiency NO_(x) Soot Efficiency [%] [%] [%] [%] [%] [%] GD100 −24.64 92.95 −1.63 1.1 −38.46 2.72 GD75 −18.21 52.6 −1.36 −0.22 −33.37 2.45 GD50 −12.32 6.17 −1.63 0.24 −35.98 0.27

Table IV lists experimental emission results of tests performed om the Cummins ISX 15 compression ignition engine, in this case listing both absolute values and relative variation from a 100% diesel baseline. The test results on the Cummins engine with the higher light fraction percentage-fuels (GD100, GD75) indicate that CO2 emissions decrease 3.25-4.25%, and soot decreases more markedly between 27-45%, at approximately constant NOx and efficiency. Accordingly, the fuel composition of the present invention can be seen as a significant improvement over commercial diesel in terms of emission reduction.

TABLE IV Absolute Values Values Relative to Commercial Diesel Commercial Commercial Diesel GD100 GD75 GD50 Diesel GD100 GD75 GD50 NO_(x) [g/kWh] 4.53 4.65 4.64 5.07 0.00 2.65 2.43 11.92 Soot [g/kWh] 0.04 0.022 0.029 0.026 0.00 −45.00 −27.50 −35.00 HC [g/kWh] 0.08 0.13 0.13 0.12 0.00 62.50 62.50 50.00 CO [g/kWh] 0.37 0.4 0.41 0.35 0.00 8.11 10.81 −5.41 BTE [%] 42.6 42.3 42.5 42.6 0.00 −0.7 −0.23 0.00 BSFC [g/kWh] 197.7 192.9 193.3 193.5 0.00 −2.43 −2.23 −2.12 CO₂ [g/kWh] 610.9 585.3 591.1 595.3 0.00 −4.19 −3.24 −2.55

Fuel variants according to the present invention can provide global and local pollutant reduction without requiring software modifications while leveraging existing diesel engine hardware. It is believed that in certain implementations, adjustments can be made to certain diesel equipment to better accommodate the novel formulation. For example, the caps of diesel tanks can be modified to be airtight, and additional mechanisms can be employed to balance the pressure inside the tank.

It is to be understood that any structural and functional details disclosed herein are not to be interpreted as limiting the systems and methods, but rather are provided as a representative embodiment and/or arrangement for teaching one skilled in the art one or more ways to implement the methods.

It is to be further understood that like numerals in the drawings represent like elements through the several figures, and that not all components and/or steps described and illustrated with reference to the figures are required for all embodiments or arrangements

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Terms of orientation are used herein merely for purposes of convention and referencing, and are not to be construed as limiting. However, it is recognized these terms could be used with reference to a viewer. Accordingly, no limitations are implied or to be inferred.

Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having,” “containing,” “involving,” and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications will be appreciated by those skilled in the art to adapt a particular instrument, situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. 

What is claimed is:
 1. A light fraction fuel composition for compression-ignited engines comprising: about 25 v/v % to about 50 v/v % commercial diesel fuel; about 40 v/v % to about 69 v/v % straight run heavy naphtha; about 5 v/v % to about 10 v/v % n-butanol; and about 0.2 v/v % to about 1.7 v/v % 2-Ethylhexyl nitrate.
 2. The light fraction fuel composition of claim 1, wherein the relative percentages of commercial diesel fuel and straight run heavy naphtha are controlled to obtain a cetane number of at least 51 for a selected engine.
 3. The light fraction fuel composition of claim 1, wherein the relative percentages of commercial diesel fuel and straight run heavy naphtha are controlled to obtain a Reid vapor pressure in a range of about 7.28 PSI and about 10.88 PSI for a selected engine.
 4. The light fraction fuel composition of claim 1, wherein the relative percentages of commercial diesel fuel and straight run heavy naphtha are controlled to obtain a boiling point range of about 30 C (initial) to about 350 C (final).
 5. The light fraction fuel composition of claim 1, including about 26 v/v % commercial diesel, about 68 v/v % straight run heavy naphtha, about 5 v/v % n-butanol and about 1.0% 2-Ethylhexyl nitrate.
 6. The light fraction fuel composition of claim 1, including about 45 v/v % commercial diesel, about 49 v/v % straight run heavy naphtha, about 5 v/v % n-butanol and about 1.0% 2-Ethylhexyl nitrate.
 7. A light fraction fuel composition for compression-ignited engines comprising: about 0 v/v % to about 50 v/v % commercial diesel fuel; about 40 v/v % to about 94 v/v % straight run heavy naphtha; about 5 v/v % to about 10 v/v % n-butanol; and about 0.2 v/v % to about 1.7 v/v % 2-Ethylhexyl nitrate.
 8. The light fraction fuel composition of claim 7, wherein the relative percentages of commercial diesel fuel and straight run heavy naphtha are controlled to obtain a cetane number of at least 51 for a selected engine.
 9. The light fraction fuel composition of claim 7, wherein the relative percentages of commercial diesel fuel and straight run heavy naphtha are controlled to obtain a Reid vapor pressure in a range of about 7.28 PSI and about 10.88 PSI for a selected engine.
 10. The light fraction fuel composition of claim 7, wherein the relative percentages of commercial diesel fuel and straight run heavy naphtha are controlled to obtain a boiling point range of about 30 C (initial) to about 350 C (final).
 11. The light fraction fuel composition of claim 7, including about 24 v/v % commercial diesel, about 70 v/v % straight run heavy naphtha, about 5 v/v % n-butanol and about 1.0% 2-Ethylhexyl nitrate.
 12. The light fraction fuel composition of claim 7, including about 45 v/v % commercial diesel, about 49 v/v % straight run heavy naphtha, about 5 v/v % n-butanol and about 1.0% 2-Ethylhexyl nitrate. 